Abstract: An apparatus is provided for converting an air flow into useful mechanical work by means of a reciprocating blade means. The preferred blade means comprises a plurality of lightweight, airfoil shaped blades mounted in a stack for moving a carrier associated therewith along a rectilinear path. A reversing means reverses the angle of attack of the blade at each end of the carrier travel. The wind machine is generally of rectangular shape and can be readily used in combination with high-rise buildings to provide a useful work output.